Rifampicin Pulmospheres for Pulmonary Delivery

Dry powder inhalation formulations of rifampicin were prepared. Spray drying was used to prepare pulmospheres and their physicochemical characteristics were evaluated. Spray dried pulmospheres containing rifampicin were mixed with inhalable lactose for preparing dry powder inhalation formulations. These formulations were further characterized to evaluate the feasibility of developing effective treatments for pulmonary tuberculosis.

Tuberculosis is most commonly caused by the deposition of bacteria, Mycobacterium tuberculosis in the lungs.Pulmonary tuberculosis is characterized by alveolar macrophages containing large number of bacilli that are typically about 5 µm in length, facilitating their entry into the lower airways.Antitubercular drug delivery systems can be administered by the pulmonary route to avoid frequent dosing.It could be helpful in direct drug delivery to the lungs, drug targeting to alveolar macrophages, reducing systemic toxicity of the drug.Biodegradable polymers like PLGA are capable of sustained drug release over days to several weeks.Therefore in present study, an attempt was made to develop dry powder inhalation (DPI) formulations of rifampicin (RIF) for pulmonary delivery.DPI formulations of spray dried RIF and of RIF pulmospheres with Poly(DL-lactide-co-glycolide) polymer (75:25) have been developed

MATERIALS AND METHODS
Rifampicin (Lupin Ltd., Mumbai, India); Pharmatose 325 (DMV international) and Lactohale (Borculo) were generous gift samples.Biodegradable polymer PLGA (75:25) with viscosity of 0.19 dl/g in chloroform as reported by the manufacturer was procured from Birmingham polymers.

Development of conventional spray dried RIF:
RIF solutions of concentration of 2-40 mg/ml were prepared in dichloromethane and spray dried using Labultima Mini Spray Dryer.Process parameters were optimized using 2 2 factorial design.Effect of process parameters on particle size was studied (fi g. 1).

Preparation and characterization of RIF-loaded pulmospheres:
Spray drying technology was used to prepare pulmospheres.The solution of polymer containing drug was spray dried to generate polymer-coated particles.Developed pulmospheres were evaluated for physiochemical properties like particle size, surface

Formulation development of DPI:
Spray dried RIF/pulmospheres of RIF were mixed with inhalable lactose in varying ratios and developed DPI formulations were characterised (Table 1).The optimum ratio of coarse lactose to fi ne lactose that gives maximum respirable fraction was selected (fi g. 2).In vitro aerolisation behaviour of the formulations was evaluated using a Rotahaler, and the performance was characterised based on uniformity of emitted dose and aerodynamic particle-size distribution (respirable fraction (RF), as a percentage of nominal dose (RFN) and emitted dose (RFE).DPI formulations of spray dried RIF and PLGA-based RIF Pulmospheres were compared in terms of respirable fraction delivered (fi g. 3).

In vitro release studies:
Release studies were performed by dialysis method.The diffusion cell was kept at 37° with continuous stirring at 100 rpm and RIF was analyzed spectrophotometrically at 475 nm.Coefficient of correlation from plots of Q vs. t, (cumulative % drug release vs. time), log of percent drug retained vs. t and Q vs. square root of t were calculated to determine drug release.

RESULTS AND DISCUSSION
Optimum process parameters for spray dried RIF were inlet temperature (55 o ), aspirator rate (60 l/min), feed rate (10 ml/min) and optimum concentration was 2 mg/ml (fig.1).DPI formulations were developed using various grades of inhalable lactose like pharmatose and Lactohale in various combinations.The effect of particle size of excipients on respirable fraction of RIF was assessed (Table 1, fig. 2).Pulmospheres of RIF were prepared with PLGA (1:1, drug:polymer ratio) with 96% v/v entrapment efficiency.Developed PLGA porous pulmospheres were characterized by SEM analysis (fi g. 4) and for particle size (fi g. 5), % drug entrapment and %FPF (Table 2).DSC studies confirmed no interaction between drug and polymer (fig.6).Regression coeffi cients (near to 1) for zero order, fi rst order and November -December 2009 *Address for correspondence E-mail: mohitmehta30@gmail.com

Mehta et al.: Novel Nasal in situ Gelling System
In situ gelling systems based on temperature-dependent phase transition containing pheniramine and phenylephrine were developed using combination of Poloxamers, different cellulose polymers (HPMC) and xanthan gum.The formulations were tested for in vitro gelation, appearance, pH, drug content, in vitro drug release, mucoadhesive strength, preservative effi cacy and stability.In vitro release studies revealed signifi cant prolonged released of both drugs up to 24 h as against only 2 h with drug solution.Formulations were found to stable over period of 3 months.In vivo nasal residence time of in situ gel by gamma scintigraphy was found to be signifi cantly higher (6 h) in comparison to drug solution (15 min).It can be concluded that Poloxamers in combination with HPMC are suitable to develop stable, safe in situ temperature-based mucoadhesive gelling systems with prolonged nasal residence time.

Key words: Nasal in situ gelling systems, mucoadhesion, gamma scintigraphy, nasal residence time
Almost 15% of world's population suffers from chronic sinusitis.Treatment for sinusitis is directed towards relief of symptoms; drugs used include antihistaminics, antibiotics, corticosteroids and decongestants.Several formulations for relief of sinusitis are approved for intranasal aerosol delivery by nasal spray pumps or by pMDI systems.These formulations require frequent administration due to nasal mucociliary clearance.Also, nasal decongestants may dry out the affected areas and damage tissues, and with prolonged use they often become ineffective.The tendency is to then increase the frequency of use to as often as once an hour which can cause rebound effect.The present work aimed to develop sustained release in situ gelling formulations of antihistaminic and decongestant combination for intranasal administration, for treatment of sinusitis, and there by overcome the frequent dosing required with conventional nasal formulations.
In situ gelling systems based on temperaturedependent phase transition were developed using combination of Poloxamers.In order to reduce concentrations of above polymers and to develop bioadhesive property, different cellulose polymers (HPMC) and xanthan gum were tried in various Higuchi's model equations confi rmed release by fi rst order (R 2 =0.97887) (fig.7).Spray dried RIF and Pulmospheres exhibited excellent fl ow and dispersion from passive DPIs while pulmospheres released for longer period of time.In vitro characterization has predicted highly efficient lung delivery of RIF for treatment of pulmonary tuberculosis.